A fundamental question in managing sciatica pain remains unanswered: Is chronic sciatica pain mediated by persistent inflammation? Sciatica refers to back pain with a radicular component. Sciatica pain accounts for up to 40% of all back pain, which is a leading cause of lost workdays in the US, costs employers an estimated $7.4 billion/year, and is the main reason for disability in Americans under 45 years old. Among the main causes of sciatica pain are intervertebral disk displacement and stenosis of the intervertebral foramen producing inflammation of neural structures and severe pain. Interlaminar and transforaminal injection of epidural steroids are extensively used to treat sciatica. The rationale is that reduction in regional inflammation promoted by steroids will lead to improvement of symptoms. However, there is very limited evidence on the association between structural abnormalities in the vertebral column, corresponding inflammatory changes around nerve roots, and sensory or motor symptoms associated with back and sciatica pain. There is also significant doubt on the effectiveness of steroid injections for treatment. Magnetic resonance imaging (MRI) is the main imaging technique to assess structural changes associated with pain of spinal origin. Recently, advances in Positron Emission Tomography (PET) introduced the tracer [11C]PBR28 to specifically investigate neuroinflammation. Availability of PET/MRI cameras offers a unique opportunity to study the association between neuroinflammation and structural changes in this major medical problem. We propose to use PET/MRI with [11C]PBR28 to study the association between inflammation, structural changes, symptoms and treatment outcome in patients with sciatica. The ability to image neuraxial inflammation developed in this study has the potential to revolutionize the diagnosis and treatment of low back pain. We plan to perform a pilot study of [11C]PBR28 PET/MRI of the lumbosacral spine in patients with sciatica pain to establish this methodology and explore the role of this technology in guiding clinical treatment of sciatica pain.